Direct current to direct current (DC-DC) converters are used to convert a direct current source from one voltage level to another. DC-DC converters are widely used in portable electronics, such as mobile phones, personal data assistants (PDAs), and laptops, to convert a voltage supplied by a battery into a supply voltage or control signal used by other functional blocks.
DC-DC converters may be used to generate control signals for radio-frequency (RF) antenna switches. Traditionally, RF antenna switches are used in pairs with one of the switches being in series with an RF signal and the other switch being in shunt with the RF signal. These RF antenna switches are manufactured using depletion-mode pseudomorphic high electron mobility transistor (pHEMT) devices in a gallium arsenide (GaAs) die.
These pHEMT-device RF antenna switches are switched off with a negative gate voltage, and switched on with a positive gate voltage. As such, complementary control signals are needed for the pair of RF antenna switches so that one of the devices in the pair is on while the other is off. Furthermore, level-shifters are used to translate a positive voltage reference and a negative voltage reference into the positive gate voltage and negative gate voltage to ensure that the correct voltage levels are supplied to gates of the RF antenna switches.
Currently, one of the methods to generate this negative voltage reference is to design a positive voltage doubler in the antenna switch GaAs die and use a large amount of capacitance to convert this positive voltage into the appropriate negative voltage. This design uses a large amount of costly GaAs die area, since complementary n-type and p-type switching devices are not available in GaAs technology. Additionally, the positive voltage doubler design results in a large current drain due to the extra circuitry needed to attain functionality using only one type of semiconductor device and the gate leakage current that is an artifact of the pHEMT technology. Furthermore, there is wide variation in the performance of the generated negative voltage. This variation negatively affects the overall performance of an antenna switch module incorporating such a design.